The present invention relates to a speech waveform coding system which is one of speech signal coding systems and, more particularly, to a speech coder and a speech decoder for use in an adaptive delta modulation (hereinafter abbreviated to ADM) coding system.
The ADM coding system is employed for digital mobile radio communication and the like because of robustness to coding errors during transmission and advantages of easy synchronization, small size and low power consumption over other coding systems.
In the conventional system, however, when a transmitted signal is erroneously changed from a state "0" to a state "1", deterioration of the speech quality is particularly serious.